Is it allowed ti use some low range and low power laser pointer just for calibrating cameras in 3 minutes preparation time?

We will use it just to know where camera lens is approximately looking and then turn it off so the laser pointer won't be working during the match time. Also it won't be pointed to the crowd during the calibration, we will point it just on some table elements.

Yes it's allowed to use a laser pointer to calibrate your camera target before strating the match. Especially if the laser is not projected outside of the playing area.
But the class constraint is exactlly the same for all laser, on robots, on beacons, everywhere, and it's not linked to the using time period.

Remember the chapter F.5.b:

Only the laser class definitions (defined according to the international standard IEC60825) will be considered. Teams using lasers will have to provide a document from the manufacturer indicating the class of the device (this information is normally systematically available on the system itself).

On the basis of this classification, class lasers:
* 1 and 1M are accepted without restriction
* 2 are tolerated if the laser beam is never projected outside the playing area
* 2M, 3R, 3B and 4 are formally prohibited.

You must have documentation with your laser pointer to proof the class of the device.
So in case of your exemple (laser pointer on Aliexperss), I'm not sure that you can proof it's a low power laser (class 1, 1M or 2).

I recommend you to find an appropriate laser pointer, conform to the requirements of the contest.